1. Field of the Invention
This invention generally relates to a repair insert for repairing targeted defect-containing metallic structure, and more particularly to a rail insert for repairing railroad rail having a localized defect in the top portion of the rail.
2. Description of Prior Art
Railroads must maintain their track to ensure safe operation of trains. Some of this maintenance centers on the repair of rail defects. Railroad rails may be manufactured with internal defects or, as a result of fatigue, develop defects. These defects are commonly located using non-destructive test methods. The Federal Railway Administration (FRA), for example, mandates periodic ultrasonic testing of railroad rails to locate defects in the rail. When a defect is found, a repair must be made to the track structure. It has been noted that many of these defects are located in the top portion of the rail or within the rail head.
There are two common welding processes used to facilitate the repair of defects in railroad rails. These processes are the thermite welding process and the flash-butt welding process. Rails repaired by a flash-butt weld are typically stronger and higher in quality than those repaired by a thermite weld. Repairs made by the thermite process are initially less costly, however, due to the relatively higher labor and equipment or components cost(s) required by the flash-butt process. Rails may also be temporarily repaired through the use of joint bar splices. Overall rail integrity is best maintained, however, by having the lowest number of joints (mechanical or welded) in track.
State of the art rail repair directed at repairing defects has typically involved removing a length of rail, (typically 13 to 19 feet in length) localized around the defect, from the existing rail. The removal of the rail length thus creates a significant gap in the rail. A so-called “rail plug” is then inserted in the resulting gap to make up for the bulk of the rail length removed. A weld is then made at each end of the rail plug, welding the rail plug to the existing rail, and creating a continuously welded rail.
A thermite weld can be used to weld the existing rail to the rail plug. A rail plug is cut to a length approximately two inches shorter than the length of the rail containing the defect, which is being cut out. The repair plug is placed into the gap. A sand mold is attached to both the existing rail and the rail plug around an approximate one-inch gap between the end of the existing rail and the end of the rail plug. The thermite material is contained in a crucible located immediately above the sand mold. After the mold is pre-heated, the thermite charge is ignited. The thermite charge creates molten steel, which pours into the sand mold.
As the thermite material solidifies, it forms a casting, which bonds to, and is contiguous with, both the existing rail and the rail plug. In this manner, the rail plug is welded to the existing rail to form a continuous section. A second thermite weld is made at an approximate one-inch gap at the opposite end of the rail plug, joining the rail plug to the existing rail. The area of the rail containing the thermite weld material is not as strong as and is not of the same quality as normal rail steel. As such, the thermite welds typically require subsequent repairs in order to maintain the railroad rail in safe condition. This method also requires the repair crew to transport a rail plug to the repair site and the section of rail containing the defect away from the site.
A flash-butt weld can also be used to weld the existing rail to the rail plug. A rail plug is cut to a length approximately three inches longer than the length of the rail containing the defect, which is being cut out. Rail anchors are removed from the existing rail until the gap created by the removal of the defect containing rail plug is three inches longer than the defect containing rail plug. This can only occur when the current rail temperature (CRT) is below the neutral rail temperature (NRT). The rail plug is put in to the gap created by the removal of the defect containing rail plug and gap growth created by the removal of anchors.
The rail ends to be welded are aligned. A flash-butt weld welderhead is clamped across the abutment of the rail plug and the existing rail, and the flash-butt welding cycle is carried out. The welderhead passes a high current across the interface between the existing rail and the rail plug. The current produces arcing between the mating surfaces. As the cycle progresses and sufficient heat has been generated, the welderhead forges the two pieces of rail together to essentially form a single continuous rail. A shear die is then pushed across the weld to return the weld profile to the rail contour. The flashing away of the rail and the forging of the rail consume about one and one half inches of rail from the rail and the rail plug.
The rail ends at the other end of the rail plug are aligned. The flash-butt welderhead is moved to the other end of the rail plug and clamped across the abutment of the rail plug and the existing rail. The rails are stretched to close the gap (which was generated by the making of the initial weld and subsequent moving the rail plug) and the flash-butt weld cycle is carried out. Rail anchors are then replaced on to the existing rail. As such, the flash-butt welding process is typically more costly than the thermite process. This method also requires the repair crew to transport a rail plug to the repair site and the section of rail containing the defect away from the site.
Regardless of the repair weld process used, there is a need to maintain the NRT. The NRT is the temperature at which the rail contains no longitudinal thermally-induced rail stresses. The track is designed to not allow the rails to contract and expand in response to environmental temperature changes. It is designed to constrain the rail and allow the rail to develop tension and compression. The amount of tension or compression is determined, in part, by the difference between NRT and the CRT.
When a repair is accomplished by installing a rail plug, it is unlikely that the rail plug installed will be of the exact length necessary to maintain the NRT of the rail, and the NRT of the rail is thus altered. As such, the segment will have a different NRT than desired. Notably, management of the NRT could be simplified if no rail length is removed during the repair of a defect in the rail.
It is further noted that when rail plugs are installed using either the thermite weld or the flash-butt weld processes, the rail is taken out of service. Thermite welding and flash-butt welding trucks need to occupy the track. This prevents the railroad from running revenue-producing trains. The installation of a rail plug and the resulting two necessary welds uses valuable track time and this repair time needs to be kept to a minimum.
Joint bar splices are, essentially, reinforcing clamp means applied to the rail adjacent to the repair. A joint bar splice is used when there is not enough time to perform a complete repair by welding or when other repair materials are not available. A joint bar splice, by government regulation, is a temporary repair and must be replaced in about 90 days. The joint bar splice thus reduces the operational limit of the rail in the repair area.
U.S. Pat. No. 7,520,415, which issued to Kral et al. discloses a further Method of Repairing Rail, which disclosure attempted to address the noted rail repair shortcomings. The '415 patent describes a system or method comprising at least the following steps: identifying and locating a defect in the rail, removing the defect by removing material from the rail surrounding the defect in at least the head section so as to form a void and a rail void interface while maintaining continuity of the rail, filling the void with molten metal having a high carbon content and causing the molten metal and the rail void interface to bond.
The molten metal may be produced by gas shielded arc welding. The carbon content of the molten metal is near that of the rail to decrease carbon migration from the rails. High carbon welding electrode is used in the welding of high strength steel using gas shielded arc welding techniques whereby a plurality of beads of molten weld material join together rail ends or fill a slot in a rail for repair purposes. The high carbon electrode avoids producing adjacent soft and brittle areas across a weld fusion line, which results from migration of carbon from the carbon rich high strength steel to the lower carbon and highly alloyed weld deposit.
The foregoing methodology described by Kral et al., while notably superior to certain aspects of the thermite and flash-butt rail repair/welding techniques described hereinabove, nevertheless also suffers from certain shortcomings. In this regard, it is noted that the molten metal material is a dynamically active medium, which medium presents certain difficulties in (non-ideal) application scenarios. For example, if the rail is inclined in the field, the molten pool of material becomes difficult to manage, and a proper weld is often problematic to achieve without much ado.
The prior art thus perceives a need for a rail repair method that results in a rail repair having the strength and quality of the parent rail, but without adding or consuming rail. Further, the prior perceives a need for a rail repair method which reduces the total number of welds in the remaining rail. Still further, the prior art perceives a need for a rail repair method which reduces the amount of materials and equipment that must be transported to and from the repair site.
Other prior art needs include a need for a rail repair method that eliminates the use of temporary joint bar splices. The prior art further perceives a need for a rail repair method that does not necessitate the relatively costly and time-consuming removal of a section of rail. The present invention attempts to address the foregoing by providing a cost effective, time-efficient rail repair method which minimizes the amount of time that the rail is out of service to revenue-producing trains, and which method greatly reduces the manpower otherwise required to effect state of the art type repairs.